A giant magnetoresistive (GMR) element formed of a multilayer film including a ferromagnetic layer and a nonmagnetic layer, and a tunnel magnetoresistive (TMR) element in which an insulating layer (a tunnel barrier layer, a barrier layer) is used as a nonmagnetic layer are known. Generally, although a TMR element has a higher element resistance as compared with a GMR element, a magnetoresistance (MR) ratio of a TMR element is larger than an MR ratio of a GMR element. Therefore, attention has been focused on a TMR element as an element for magnetic sensors, high frequency components, magnetic heads, and magnetic random access memories (MRAMs).
In an MRAM, data is read and written by utilizing characteristics in which the element resistance of a TMR element changes as magnetization directions of two ferromagnetic layers sandwiching an insulating layer change. As a writing method of MRAMs, a method of performing writing (magnetization reversal) by utilizing a magnetic field generated by a current, and a method of performing writing (magnetization reversal) by utilizing a spin transfer torque (STT) generated by causing a current to flow in a lamination direction of a magnetoresistive effect element are known. Although the magnetization reversal of the TMR element using an STT is efficient when considered from the viewpoint of energy efficiency, a reversal current density for causing magnetization reversal is high. From the viewpoint of a long life span of the TMR element, it is preferable that the reverse current density be low. The same applies for GMR elements.
In recent years, attention has been focused on a magnetization reversal method in which a pure spin current generated by a spin Hall effect is utilized as a means for reducing the reversal current in a mechanism that is different from an STT (for example, see Non-Patent Document 1). A pure spin current generated by the spin Hall effect induces a spin-orbit torque (SOT) and the SOT causes magnetization reversal to occur. The pure spin current is generated when the same number of upward spin electrons and downward spin electrons flow in opposite directions to each other, and thus flows of electric charge cancel out. Therefore, a current flowing through the magnetoresistive effect element is zero, and thereby realization of a magnetoresistive effect element with a small reversal current density can be expected.
According to Non-Patent Document 2, it is reported that a reversal current density using the SOT method is approximately the same as a reversal current density using the STT method. However, the reversal current density reported in the present SOT method is insufficient for realizing high integration and low energy consumption, and there is room for improvement.
As a material used for a spin-orbit torque wiring (a wiring which induces an SOT to generate a pure spin current) of the magnetoresistive effect element in an SOT method, heavy metal materials such as Ta as used in Non-Patent Document 2 are exemplary examples. Since such heavy metal materials have a high electrical resistivity, high power consumption is also a problem when thin metal or a thin wire is used.